1. Field of the Invention
The present invention relates to new stabilizer products for lubricant oils and greases having perfluoropolyether structure. The so stabilized lubricants are resistant to degradation and do not corrode the metals, such as, e.g., Al, Ti, V, or their alloys, or steels at temperatures comprised within the range of from -50.degree. C. to &gt;+300.degree. C., under oxidizing atmosphere and when the metal or alloy and the lubricant, either as oil or as grease, are in contact with each other.
More particularly, the invention relates to stabilizers on the basis of arylphosphines or of derivatives of arylphosphines, possibly having an oxygen or sulphur atom directly bonded to the phosphorus atom, containing at least one perfluoroether chain in their molecule. Further object of the invention is to provide a process which can be easily implemented on industrial scale and allowing the above said stabilizers to be produced with considerable reductions in production costs.
2. Description of the Prior Art
It is known that the use of fluids having polyperfluoropolyether structure at high temperature under an oxidizing atmosphere causes with time, generally within a time period of about twenty hours, a progressive degradation of the fluid, when this is in contact with metals or alloys. The degradation depends both on the conditions under which the fluid is used, and on its chemical structure.
For example, perfluoropolyether fluids marketed under the trade name Fomblin Z.RTM. result less stable than the corresponding Fomblin Y.RTM. or Krytox.RTM. products, when they are used under an oxidizing atmosphere at high temperature, e.g., at temperatures comprised within the range of from 200.degree. C. to 300.degree. C., in the presence of titanium or of titanium-based metal alloys.
From the prior art perfluoroarylphosphines, disclosed in U.S. Pat. No. 3,393,151 and 3,499,041, and used as corrosion and degradation inhibitors in perfluoropolyether fluids, are known. They are characterized by having three perfluorinated benzene rings bonded to the phosphorus atom or to the phosphinoxido group (U.S. Pat. No. 3,393,151), or the perfluorinated benzene rings can be differently substituted with always completely fluorinated groups of the type of: C.sub.n F.sub.2n+1, C.sub.6 F.sub.5, C.sub.6 F.sub.5 O, C.sub.n F.sub.2n+1 -C.sub.6 F.sub.4, C.sub.n F.sub.2n+1 -C.sub.6 F.sub.4 O, with n being comprised between 1 and 8.
Although such products perform their action as inhibitors of metal corrosion and of perfluoropolyether degradation, as hereinabove mentioned, they are however poorly soluble in perfluoropolyethers at low temperatures, and moreover some of these compounds result volatile at high temperature.
Furthermore, in U.S. Pat. No. 3,567,803 are described stabilizers of the class of phosphinates having the following structural formulae: EQU R.sub.f O(C.sub.3 F.sub.6 O).sub.m CFX--CH.sub.2 O--P(:O)(C.sub.6 H.sub.5).sub.2 EQU (C.sub.6 H.sub.5).sub.2 --P(:O)--OCH.sub.2 --CFX(C.sub.3 F.sub.6 O).sub.m CFX--CH.sub.2 O--P(:O)(C.sub.6 H.sub.5).sub.2
wherein R.sub.f is a perfluoroalkyl chain containing from 1 to 6 carbon atoms, m is an integer comprised between 3 and 50, X is --f or --CF.sub.3. Such compounds are used as inhibitors of high temperature degradation and corrosion in hydraulic and lubricant fluids having perfluoropolyether structure. Phosphinates of this type, however, do not show good stability characteristics, and moreover have poor low-temperature solubility in the fluids to be stabilized.
Moreover, the amount of phosphinate to be added to perfluoropolyether, according to the said patent, must be quite high, of the order of 5-10% by weight. Amounts of stabilizer as high as these, besides impairing the fluodynamic characteristics of the perfluoropolyether fluid, render still more critical the low-temperature solubility of these additives in perfluoropolyethers, and this causes considerable storage problems, due to the precipitation of the stabilizer. Furthermore, these stabilizers, even when they are stored separately, must be kept under conditions as anhydrous as possible, because they are very sensible to the hydrolysis.
All these drawbacks limit the application thereof as stabilizers of perfluoropolyethers.
Arylphosphines, not necessarily completely fluorinated, are also known from U.S. Pat. No. 4,011,267, to be used as stabilizers for the above mentioned applications, having formulae of ##STR1## type, wherein one R radical is a perfluoroalkylether of general formula EQU (R.sub.f OR.sub.f --CF.sub.2 --),
the other two R radicals are F and n ranges from 1 to 3.
The group R.sub.f OR.sub.f can be of the type EQU C.sub.3 F.sub.7 O[CF(CF.sub.3)CF.sub.2 O].sub.x CF(CF.sub.3)-- EQU C.sub.2 F.sub.5 O(CF.sub.2 CF.sub.2 O).sub.y CF.sub.2 -- EQU CF.sub.3 O(CF.sub.2 O).sub.z CF.sub.2 --,
wherein x, y, z are zero or an integer ranging from 1 to 20, preferably from 1 to 4 included.
These stabilizers are prepared by starting from dibromotetrafluorobenzene, which is reacted with a Grignard compound, e.g., ethylmagnesium bromide; a treatment is then carried out with a cuprous halide. The organocuprous compound so obtained is reacted with a perfluoroacyl halide ##STR2## a ketone is so obtained, which is reacted with SF.sub.4 in the presence of anhydrous HF.
The so functionalized bromobenzene is treated with butyllithium and subsequently with PCl.sub.3 or dichlorophenyl phosphine or chlorodiphenylphoshine, to yield the products according to the patent.
Such a preparation method is not much interesting from a practical viewpoint, in that it requires very complex reactions, which cannot be proposed for a full-scale application. By this method, products are obtained in very small amounts at of very high cost.
Arylphosphines, disclosed in U.S. Pat. No. 4,454,349, are moreover known, of general formula: ##STR3## wherein the group R.sub.f OR.sub.f, similarly to as in the above mentioned patent, can be of the type EQU C.sub.3 F.sub.7 O[CF(CF.sub.3)CF.sub.2 O].sub.x CF(CF.sub.3)-- EQU C.sub.2 F.sub.5 O(CF.sub.2 CF.sub.2 O).sub.y CF.sub.2 -- EQU CF.sub.3 O(CF.sub.2 O).sub.z CF.sub.2 --,
and the indexes x, y, z are 0 or an integer of value of from 1 to 20, preferably of from 1 to 4 included.
Such products are obtained by reacting a dibromobenzene with butyllithium, the compound obtained is then reacted with a perfluoropolyether, having an esther as the end group, to obtain the ketone; the carbonyl group is then fluorinated by SF.sub.4 and HF. The so-obtained product is treated with butyllithium and then with PCl.sub.3 to obtain the triarylphosphinic compounds.
Such arylphosphines have the same stabilizing properties as of those disclosed in prior U.S. Pat. No. 4,011,267, but they are obtained by a more simplified process, and starting from cheaper precursors, that considerably reduces the production costs, even if these remain however very high.
Also this process results not suitable to a full-scale passage, in that it contains, as critical and essential step, the reaction of fluorination of C.dbd.O group by SF.sub.4 and HF.
Such a fluorination by SF.sub.4 and HF involves problems both as for the equipment required, and as for the control of the fluorination reaction, due to the following reasons:
(1) low reaction rates; PA1 (2) use of high pressure and temperature values, respectively of the order of 70-80 atm, and T=150.degree.-170.degree. C.; PA1 (3) dangerousness of SF.sub.4 and HF reactants under the indicated temperature and pressure conditions; PA1 (4) need for special materials for plant construction; PA1 (5) extreme difficulty in monitoring the fluorination proceeding, due to the physical-chemical characteristics of the reactants and by-products (SF.sub.4 and SOF.sub.2) used as the test compounds for the check of the proceeding of the reaction; PA1 R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, equal to, or different from each other, can be --H, --F, --CF.sub.3, --B--R.sub.11, with the constraint that at least one of the various R.sub.1 -R.sub.5 groups on at least one of benzene rings is a --B--R.sub.f1 radical, wherein R.sub.f1 is: PA1 (a) Z--CF.sub.2 O(C.sub.3 F.sub.6 O).sub.m (CFXO).sub.n --CFY--, wherein PA1 X=--F, --CF.sub.3 ; PA1 Y=--F, --CF.sub.3 ; PA1 Z=--F, --CF.sub.3 or --CF.sub.2 --CF.sub.3 ; in this second case n=0 and Y=--CF.sub.3 ; PA1 m and n are integers, with m being comprised between 1 and 30 and n being comprised between 0 and 10, and the molecular weight of R.sub.f1 is comprised withn the range of from 135 to 6500 and (C.sub.3 F.sub.6 O) and (CFXO) units are randomly distributed along the chain; PA1 said chains are obtained according to UK Pat. No. 1,104,482; PA1 (b) Z--(CF.sub.2 CF.sub.2 CW.sub.2 O).sub.p -- PA1 wherein z has the meaning described above, W is H or F and p is an integer from 1 to 30; said chains are obtained according to EP Appln. 148,482; PA1 (c) D--(CF.sub.2 CF.sub.2 O).sub.q -- PA1 wherein D is --CF.sub.3 or --C.sub.2 F.sub.5, q is an integer from 1 to 30; PA1 said chains are obtained according to U.S. Pat. No. 4,523,039; ##STR5## wherein R.sub.6, R.sub.7, R.sub.8, R.sub.9, R.sub.11 are alkyl radicals containing from 1 to 3 carbon atoms, R.sub.6, R.sub.7 and R.sub.8 can be also hydrogen; R.sub.10 is an alkylene radical of from 1 to 3 carbon atoms; ##STR6## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.12, R.sub.13, R.sub.14, R.sub.15, equal to or different from each other, can be --H, --F, --CF.sub.3, --B--R.sub.f1 ; PA1 A, B, R.sub.f1 have the above exposed meaning; PA1 R.sub.f2 is: PA1 (d) --CF.sub.2 O(C.sub.2 F.sub.4 O).sub.p (CF.sub.2 O).sub.q --CF.sub.2 --, PA1 wherein p and q are integers different from zero, and the p/q ratio ranges from 0.5 to 2, preferably from 0.5 to 1.5, the average molecular weight being comprised within the range of from 300 to 7000; said chains are obtained according to U.S. Pat. No. 3,715,378; ##STR7## wherein r is an integer from 1 to 20 and R.sub.f3 is a perfluoroalkylenic radical; PA1 said chains are obtained according to EP Appln. No. 151,877; PA1 (f) --CF.sub.2 O--(CF.sub.2 CF.sub.2 CH.sub.2 O).sub.t R.sub.f3 (OCH.sub.2 CF.sub.2 CF.sub.2).sub.t --OCF.sub.2 --, PA1 wherein R.sub.f3 has the meaning described hereinabove and t is an integer from 1 to 20; PA1 said chains are obtained according to EP Appln. No. 148,482 and Italian Patent Application No. 22920 A/85; PA1 (g) --CF.sub.2 O--(--CF.sub.2 CF.sub.2 CF.sub.2 O).sub.s --CF.sub.2 --, PA1 wherein s has the meaning described hereinabove; said chains are obtained according to U.S. Pat. No. 4,523,039 and Italian Patent Application No. 22920 A/85. PA1 (h) --CF.sub.2 O--(--CF.sub.2 CF.sub.2 O--).sub.s --CF.sub.2 -- PA1 wherein s has the meaning described hereinabove; PA1 said chains are obtained according to U.S. Pat. No. 4,523,039 and Italian Patent Application No. 22920 A/85. PA1 R.sub.7 and R.sub.8 have the above indicated meaning; PA1 X=Cl, Br, I.
this latter drawback enormously reduces the potentiality of the reactor, and leads to not quantitative reactions, wich consequent need to use sophisticated rectifying equipment to separate the starting product from the end product, which have very close physical-chemical characteristics.